In the 1980s, she was Deputy Editor on The Unexplained and contributor to many other publications. She was also a regular contributor on various radio shows, including Michael van Straten and Clive Bull's on LBC and Talk Radio. She was also a television presenter for both Anglia and Southern TV.

In the early 1990s, she teamed up with fellow researcher and writer Clive Prince. Their first book, Turin Shroud: How Leonardo da Vinci Fooled History, was the first mainstream work to reveal how all the so-called miraculous characteristics of the Turin Shroud could easily be reproduced only using a pinhole camera (camera obscura), and argued that Leonardo da Vinci not only faked it, but used his own face for the model of Jesus, overlooking the fact that the first exhibition of the Shroud of Turin, authentic or not, was in 1357, almost one century before the birth of Da Vinci.

Between 1999 and his death in 2003, she and Clive Prince worked with Stephen Prior, described in book blurb as "a historian specialising in intelligence matters".

Picknett and Prince perform most of the research for their books themselves, though they are sometimes helped by several friends and fellow researchers. They have credited Keith Prince as a main contributor for their work on the Turin Shroud, Philip Coppens in The Stargate Conspiracy (published in 1999), and Robert Brydon for their work on Rudolf Hess (titled Double Standards: The Rudolf Hess Cover-Up and published in 2001).

Picknett, as well as Prince, makes a brief appearance in the film The Da Vinci Code. The pair appear on a London bus as the protagonists are travelling to the Temple Church, off Fleet Street in central London. Robert Langdon (Tom Hanks) leaves his seat to join Sophie (Audrey Tautou) at the back of the bus, and Picknett and Prince are seen sitting on the left.